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        <title>Parametric Surfaces Fun - ECHARTS-GL</title>
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        <meta name="apple-mobile-web-app-capable" content="yes"> <!-- Fullscreen Landscape on iOS -->
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        <div id="main"></div>
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            <button id="prev">Prev</button>
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        <script src="../node_modules/echarts/dist/echarts.js"></script>
        <script src="../dist/echarts-gl.js"></script>
        <script src="lib/jquery.min.js"></script>
        <script src="js/commonUI.js"></script>
        <script>
            // http://xahlee.info/surface/breather_p/breather_p.html
            var chart = echarts.init(document.getElementById('main'));

            var sin = Math.sin;
            var cos = Math.cos;
            var pow = Math.pow;
            var sqrt = Math.sqrt;
            var cosh = Math.cosh;
            var sinh = Math.sinh;
            var PI = Math.PI;

            var parametricEquations = [
                {
                    name: 'Mollusc Shell',
                    u: {
                        min: -PI,
                        max: PI,
                        step: PI / 40
                    },
                    v: {
                        min: -15,
                        max: 6,
                        step: 0.21
                    },
                    x: function (u, v) {
                        return pow(1.16, v) * cos(v) * (1 + cos(u));
                    },
                    y: function (u, v) {
                        return -pow(1.16, v) * sin(v) * (1 + cos(u));
                    },
                    z: function (u, v) {
                        return -2 * pow(1.16, v) * (1 + sin(u));
                    }
                },
                {
                    name: 'Breather',
                    link: 'http://xahlee.info/surface/breather_p/breather_p.html',
                    u: {
                        min: -13.2,
                        max: 13.2,
                        step: 0.5
                    },
                    v: {
                        min: -37.4,
                        max: 37.4,
                        step: 0.5
                    },
                    x: function (u, v) {
                        var aa = 0.4;
                        var r = 1 - aa * aa;
                        var w = sqrt(r);
                        var denom = aa * (pow(w * cosh(aa * u), 2) + aa * pow(sin(w * v), 2))
                        return -u + (2 * r * cosh(aa * u) * sinh(aa * u) / denom);
                    },
                    y: function (u, v) {
                        var aa = 0.4;
                        var r = 1 - aa * aa;
                        var w = sqrt(r);
                        var denom = aa * (pow(w * cosh(aa * u), 2) + aa * pow(sin(w * v), 2))
                        return 2 * w * cosh(aa * u) * (-(w * cos(v) * cos(w * v)) - (sin(v) * sin(w * v))) / denom;
                    },
                    z: function (u, v) {
                        var aa = 0.4;
                        var r = 1 - aa * aa;
                        var w = sqrt(r);
                        var denom = aa * (pow(w * cosh(aa * u), 2) + aa * pow(sin(w * v), 2))
                        return  2 * w * cosh(aa * u) * (-(w * sin(v) * cos(w * v)) + (cos(v) * sin(w * v))) / denom
                    }
                },

                {
                    name: 'Klein Bottle',
                    u: {
                        min: 0,
                        max: PI * 2,
                        step: PI / 20
                    },
                    v: {
                        min: 0,
                        max: 2 * PI,
                        step: PI / 20
                    },
                    x: function (u, v) {
                        var r = 3;
                        return (r + cos(v / 2) * sin(u) - sin(v / 2) * sin(2 * u)) * cos(v)
                    },
                    y: function (u, v) {
                        var r = 3;
                        return (r + cos(v / 2) * sin(u) - sin(v / 2) * sin(2 * u)) * sin(v)
                    },
                    z: function (u, v) {
                        var r = 3;
                        return sin(v / 2) * sin(u) + cos(v / 2) * sin(2 * u)
                    }
                },

                {
                    name: 'Bump Sphere',
                    u: {
                        min: -Math.PI,
                        max: Math.PI,
                        step: Math.PI / 40
                    },
                    v: {
                        min: 0,
                        max: Math.PI,
                        step: Math.PI / 40
                    },
                    x: function (u, v) {
                        var x = Math.sin(v) * Math.sin(u);
                        var y = Math.sin(v) * Math.cos(u);
                        var z = Math.cos(v);
                        delta = sin(20 * x) + sin(20 * y) + sin(20 * z);
                        return x * (1 + delta * 0.03);
                    },
                    y: function (u, v) {
                        var x = Math.sin(v) * Math.sin(u);
                        var y = Math.sin(v) * Math.cos(u);
                        var z = Math.cos(v);
                        delta = sin(20 * x) + sin(20 * y) + sin(20 * z);
                        return y * (1 + delta * 0.03);
                    },
                    z: function (u, v) {
                        var x = Math.sin(v) * Math.sin(u);
                        var y = Math.sin(v) * Math.cos(u);
                        var z = Math.cos(v);
                        delta = sin(20 * x) + sin(20 * y) + sin(20 * z);
                        return z * (1 + delta * 0.03);
                    }
                },

                {
                    name: 'Moebius Strip',
                    u: {
                        min: 0,
                        max: PI * 2,
                        step: PI / 10
                    },
                    v: {
                        min: -1,
                        max: 1,
                        step: 0.2
                    },
                    x: function (u, v) {
                        return (1 + v / 2 * cos(u / 2)) * cos(u);
                    },
                    y: function (u, v) {
                        return (1 + v / 2 * cos(u / 2)) * sin(u);
                    },
                    z: function (u, v) {
                        return v / 2 * sin(u / 2);
                    }
                }
            ];

            var currentIndex = 0;

            chart.setOption({
                tooltip: {},
                title: [{
                    text: 'Parametric Surfaces Fun',
                    subtext: 'From Virtual Math Museum',
                    sublink: 'http://virtualmathmuseum.org/Surface/gallery_o.html',
                    left: 'center',
                    textStyle: {
                        color: '#fff'
                    },
                    subtextStyle: {
                        color: '#fff'
                    }
                }, {
                    id: 'surface-name',
                    textStyle: {
                        color: '#fff'
                    },
                    bottom: 10,
                    text: parametricEquations[0].name
                }],
                visualMap: {
                    show: false,
                    dimension: 2,
                    min: -5,
                    max: 0,
                    inRange: {
                        color: ['#313695', '#4575b4', '#74add1', '#abd9e9', '#e0f3f8', '#ffffbf', '#fee090', '#fdae61', '#f46d43', '#d73027', '#a50026']
                    }
                },
                xAxis3D: {
                    type: 'value'
                },
                yAxis3D: {
                    type: 'value'
                },
                zAxis3D: {
                    type: 'value'
                },
                grid3D: {
                    axisLine: {
                        lineStyle: {
                            color: '#fff'
                        }
                    },
                    postEffect: {
                        enable: true,
                        edge: {
                            enable: true
                        }
                    },
                    light: {
                        main: {
                            intensity: 1
                        },
                        ambient: {
                            intensity: 0
                        },
                        ambientCubemap: {
                            texture: 'asset/pisa.hdr',
                            exposure: 2,
                            diffuseIntensity: 1,
                            specularIntensity: 5
                        }
                    },
                    viewControl: {
                        // projection: 'orthographic'
                    }
                },
                series: [{
                    type: 'surface',
                    parametric: true,
                    shading: 'realistic',
                    realisticMaterial: {
                        roughness: 0.4,
                        metalness: 0
                    },
                    // shading: 'albedo',
                    parametricEquation: parametricEquations[0]
                }]
            });

            function update() {
                chart.setOption({
                    title: {
                        id: 'surface-name',
                        text: parametricEquations[currentIndex].name
                    },
                    series: {
                        parametricEquation: parametricEquations[currentIndex]
                    }
                })
            }

            document.getElementById('prev').addEventListener('click', function () {
                currentIndex -= 1;
                if (currentIndex < 0) {
                    currentIndex = parametricEquations.length - 1;
                }
                update();
            });

            document.getElementById('next').addEventListener('click', function () {
                currentIndex = (currentIndex + 1) % parametricEquations.length;
                update();
            });

            window.addEventListener('resize', function () {
                chart.resize();
            });

        </script>
    </body>
</html>